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W.R. Okie and A.P. Nyczepir

Roots of dormant peach trees can grow when soil temperatures are >7 °C, which commonly occurs in the southeastern U.S. during the winter. In our tests, root growth on 1-year-old nursery trees was minimal at 7 °C, and increased with temperature up to at least 16 °C, but rootstocks varied greatly in their regeneration at a given temperature. Trees on seedling rootstocks of `Guardian™', `Halford' and `Lovell' regenerated roots more slowly than those on `Nemaguard' at soil temperatures >7 °C. The regeneration rates mirrored the relative susceptibility of these rootstocks to peach tree short life syndrome in the southeastern U.S., which is associated with parasitism by ring nematode.

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A.P. Nyczepir, B.W. Wood, and C.C. Reilly

Pecan [Carya illinoinensis (Wangenh.) K. Koch] trees exhibit nickel (Ni) deficiency in certain orchard situations. The symptoms are manifest as either mouse-ear or replant disorder and in certain situations are associated with nematode parasitism. A field microplot study of pecan seedlings treated with either Meloidogyne partityla or Criconemoides xenoplax or both found that parasitism by M. partityla can result in enhancement in the severity of mouse-ear symptoms and a reduction in foliar Ni concentration. The Ni threshold for triggering morphological symptoms in young developing foliage was between 0.265 and 0.862 μg·g–1 dry weight, while the threshold for rosetting was between 0.007 and 0.064 μg·g–1 dw. Results indicate that parasitism by M. partityla is a contributing factor to the induction of Ni deficiency in pecan and raises the possibility that nematode parasitism and Ni nutrition can be contributing factors to many plant maladies.

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T.G. Beckman, W.R. Okie, and A.P. Nyczepir

Clonally replicated peach seedlings [Prunus persica (L.) Batsch] of Lovell, Nemaguard, and four F1 selections of Lovell × Nemared were tested for field survival on a peach tree short life site. Rootstock families differed in growth, survival, and longevity. Genetic variation was similar to environmental variation for most families. Based on seedling within rootstock family, estimated broad-sense heritabilities for survival and longevity were high. The use of clonally replicated seedlings allowed the selection of apparently superior individuals from both Lovell and the other more short-lived rootstock families in a single screening.

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W.R. Okie, T. G. Beckman, and A.P. Nyczepir

Lovell rootstock is recommended for Peach Tree Short Life (PTSL) sites in the Southeast because it outlives Nemaguard. No genetic studies of PTSL tolerance have been done. Clonally replicated peach seedlings [Prunus persica (L.) Batsch] of Lovell, Nemaguard and four F1 selections of Lovell × Nemared were tested for field survival in a high density planting on a PTSL site. Rootstock families (12 seedlings × 8 ramets each) differed in growth, survival and longevity. Genetic variation was comparable to environmental variation for most families. Based on seedling within rootstock family, estimated broad-sense heritabilities for survival and longevity were high. The use of clonally replicated seedlings allowed the selection of apparently superior individuals from both Lovell and the other more short-lived rootstock families in a single screening after 6 years. Survival of Lovell at that time was 50% compared to 16-29% for other families. Across all families, all 8 ramets were dead for 21 seedlings, whereas all 8 were alive for only 3 seedlings.

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A.P. Nyczepir, W.R. Okie, and T.G. Beckman

Peach tree short life (PTSL) is associated with the presence of ring nematode, Mesocriconema xenoplax, and poor orchard management practices. Finding a noncommercial field site to evaluate rootstocks for PTSL resistance is increasingly difficult. The time needed to create a PTSL test site was investigated. In 1994, a site not planted in peaches for >80 years was identified in Byron, Ga. Analysis of preplant soil samples revealed that there were no M. xenoplax on the site. One-third of the land was planted to peach and infested with 1600 ring nematodes per tree in Spring 1994 (P2) and another one-third in Spring 1995 (P1). The remaining one-third of the land received no trees or ring nematode and served as the control (F2). In Fall 1995, trees were removed from P1 and P2 plots and all treatments were replanted to peach in 1996. In 1997, tree death resulting from PTSL occurred only in P2 (7%). By 2000, PTSL tree death reached 41% in P2, 16% in P1, and 4% in F2 plots. Nematode populations were higher (P < 0.05) in P1 (649 ring nematode/100 cm3 soil) than in F2 (221 ring nematode/100 cm3 soil) plots, whereas populations in P2 (300 ring nematode/100 cm3 soil) plots did not differ from those in P1 or F2 plots. Establishing a PTSL screening site was possible 3 years after M. xenoplax introduction; PTSL development among treatments in the subsequent planting was dependent upon cumulative population exposure of trees to M. xenoplax.

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T.G. Beckman, W.R. Okie, A.P. Nyczepir, P.L. Pusey, and C.C. Reilly

Nearly 5000 seedling trees representing more than 100 peach [Prunus persica (L.) Batsch.] and plum (Prunus spp.) lines were planted at a 4 × 0.6-m spacing in Jan. 1983, on a site with a known history of peach tree short life (PTSL) and Armillaria root rot (ARR). Trees were arranged in a randomized complete-block with eight replicates of six trees each. Beginning in Spring 1984 and each year thereafter the cause of tree death was determined. At the end of 9 years, 50% of the trees had succumbed to PTSL and 35% had been killed by ARR apparently caused by Armillaria tabescens. Analysis of the data for trees killed by ARR showed a wide range in mortality, some peach lines appeared significantly more tolerant to ARR than others. Plum lines derived from native North American species also appeared to be a potential source of improved tolerance. We did not establish whether ARR tolerance is affected by PTSL.

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Andrew P. Nyczepir, Janete A. Brito, Don W. Dickson, and Thomas G. Beckman

Six commonly known peach rootstocks (i.e., Flordaguard, Guardian®, Halford, Lovell, Nemaguard, and Okinawa) were evaluated for their susceptibility to Meloidogyne mayaguensis in the greenhouse. All rootstocks were rated as either nonhosts (highly resistant) or poor hosts (resistant) of M. mayaguensis. Lovell generally supported greater numbers of M. mayaguensis eggs per plant and eggs per gram of dry root, whereas no nematode reproduction was noted on Flordaguard rootstock (nonhost). Root galling occurred on all six rootstocks. However, reproduction as measured by number of egg masses, eggs per plant, and eggs per gram of dry root was a better measure of host resistance than number of root galls per plant.

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T.G. Beckman, G.L. Reighard, A.P. Nyczepir, and W.R. Okie

Thirteen rootstocks grafted with Redhaven peach were established on a severe peach tree short-life (PTSL) site in central Georgia. Most rootstocks tested were peach seedling types: Lovell, Nemaguard, Guardian (BY520-9), BY520-8, Boone County, Bailey and two `Tennessee Natural' selections. A seedling plum rootstock, St. Julian, was also used. Clonal type rootstocks included a peach × almond hybrid, GF677; plum, GF43 and Damas 1869; and a plum hybrid, GF655-2. Trees on Guardian displayed the best survival with only 20% mortality due to PTSL, through 7 years. In contrast, 40% of trees on Lovell succumbed to PTSL. Currently, Lovell is the recommended rootstock for PTSL-prone sites. Other rootstocks ranged from 50% to 100% mortality due to PTSL. Trees on Guardian displayed significantly higher vigor through the first 4 years following planting compared to trees on Lovell. Furthermore, trees on Guardian produced significantly greater yields than those on Lovell, in all but 1 year. Rootstock effects on tree survival, vigor, bloom and harvest dates, fruit yield and size, and suckering will be discussed.